A method and arrangement for operating an internal combustion engine is disclosed in German patent publication 196 18 385. In this publication, a control system for an internal combustion engine is described wherein the fresh air charge, which is supplied to the engine, is determined on the basis of the rpm and a measured variable. The measured variable represents the load on the engine and the fresh air charge is the air mass which is inducted by the engine per cylinder. For the control of the engine, the fresh air charge is, for example, evaluated for: the determination of a desired value for the air supply to the engine, for the computation of the ignition angle and/or for the computation of the fuel mass to be injected.
Variables such as the inducted air mass, the intake manifold pressure, the throttle flap position, et cetera, are provided as variables representing the load. For present-day control systems, at least two measuring devices are utilized, for example, a sensor for detecting the throttle flap position and a sensor for detecting the inflowing air mass or even a sensor for detecting the intake manifold pressure. Especially for engines operated with the throttle flap fully open, several of these signals (for example, throttle flap position, intake manifold pressure) are not a reliable measure for the load.
The use of sensors which measure the effective torque directly at the crankshaft of the engine is known. Such a sensor is described, for example, in the publication entitled: ATZ/MTZ Sonderausgabe System Partners 97, pages 28 to 31.
A torque model is known from U.S. Pat. No. 5,692,471 which describes the dependency of the torque of an engine on the adjusted load state, the ignition angle position, the actual adjustment of the air/fuel ratio as well as the number of inhibited or suppressed cylinders.
U.S. Pat. No. 5,484,351 discloses measures with the aid of which the lost torque of an engine is determined; that is, the combustion torque which must be developed for compensating the internal losses, the heat losses and the torque requirements of additional consumers.